Telephone-receiver.



H. R. STUART.

TELEPHONE RECEIVER. APPLIOATION IIL'ED JAN. 10, 1907.

Patented Jan. 19, 1909.

2 SHEETS-SHEET 1.

H. R. STUART.

TELEPHONE RECEIVER APPLICATION FILED JAN.10, 1907.

910,244. Patented Jan. 19, 1909.

2 SHEETS-SHEET 2 HARVE R. STUART, OF WHEELING, WEST VIRGIllIA.

TELEPHONE-RECEIVER.

Specification of Letters Patent.

Patented Jan. 19, 1909.

Application filed January 10, 1907. Serial No. 351,578.

To all whom it may concern:

Be it known that I, HARVE R. STUART, a citizen of the United States, residing at Wheeling, in the county of Ohio and State of West Virginia, have invented certain new and useful Improvements in'lelephon e-Receivers, of which the following is a full, clear, and exact description.

Ordinary voice currents are commonly produced by the well known microphone transmitter in which the varying resistance of carbon under pressure is utilized, or b a maigneticinduction transmitter in whic the uctuations or undulations are produced by magnetically induced electric currents. In either case the characteristics o'fthe voice currents are substantially the same, that is to say, the current has generally one direction of flow, but the intensityv varies continually, and in an a parently irregular way, depending on t e character of the sound transmitted. So far as I am aware these voice currents have always been reproduced into sound by the use of an iron diaphragm directly acted upon by an electromagnetdn the circuit of the voice currents. I have discovered that this form of instrument does not have the efficiency of conversion that it should. In other words, a great deal of energy is lost in the reproduction.

It is the purpose of the present invention to provide a very much more efficient form of instrument for reproducing the sound the broken line IV IV of Fig.-2,,lo0king' downward; Fig. 5 is a fragmentary perspective view, showing portions of the device.

In order that the principles underlyin the present invention may be made clear,

riefly consider the electrical conditions which are found in the ordinary operation of.

a telephone circuit. There are two initial sources of energy, one is the usual battery which may be as strong as desired, and the other is the sound wave which initially strikes more than sufficient.

'ferrotype diaphragm receiver.

igure 1 is a diagramto e ectr c motors.

the diaphragm of the transmitter. The last factor does not have very much energy, but if all of the energy can be conserved in the transmission the supply of energy will be In other words, if the energy of transmitted speech were-all conserved, the reproduced sound at the receiver would be as loud as or louder than that delivered into the transmitter. This result is not secured in practice even with a microphone transmitter, and the reason is on account of the low efficiency of the ordinary The nature of the microphone transmitter is such that it multiplies to a certain extent the energy of the sound wave in transforming it into voice currents. W1th a recelver, therefore, of ideal efficiency, and a nucrophone transmit- 'ter, the reproduced sound should be very much louder than the original voice. That these conditions are not attained in practice serves to show the very low efficiency attained by the telephone receiver of the ordinary sort. I have found that this low efficiency is largely due to three factors. first of these is the too great stiffness of the ordinary ferrotype diaphragm em loyed. The diaphragm should be so hght an elastic The that all of the energy of its vibrations goes into $5 the air rather than into intermolecular friction or internal heat, as is the case with the ordi nary fairly stiff iron diaphragm. Theordi nary iron diaphragm transforms only a very small pro ortion of its energy of vibration into soun waves. The remainder is lost in the work done in moving the molecules of the uantity of iron is presented to take care of t e magnetic flux produced by the voice cu1j-- rents. The receiver is in a sense an electric motor because it produces mechanical movement "and delivers power from an electrical current. Certain' of the same principles of should therefore be followed as apply k In other words, the iron of the movable and immovable parts ,should each be, sufficiently massive to carry the magnetic flux produced by the windings without saturation; ordinary telepilione receiver, because the diahis is not done in the phragm is so ght and thin as to imperfectly carry even the fixed flux of the usua permanent magnets. In carrying out the present invention the working parts are designed strictly in accordance with the principles of ideal efficiency, with provision for sufficiently massive iron parts to carry all the flux due to the impressed magneto motive force. A 5 third, and also very important source of ineffiency in the ordinary telephone receiver, lies in the fact that the forces which are developed by the varying magnetic fiux in the iron parts are not transformed into movement of the diaphragm. The dia hragm is quite' stifl and is necessarily c amped between fixed rings, and these act of course to owerfully dampen the vibrations of the diap ragm. The condition is analogous to the application of forces to a body which is anchored against any but a very small movement. It is evident that only such small movement will be produced instead of the large movement which would otherwise be induced by the applied forces in case the object were not anchored. These three reasons are the principal, although not all, of the causes of the very low reproductive efficiency which is secured by the ordinary telephone receiver.

I will first elucidate the broad rinciples on which the present invention is liased, by the aid of diagrams, and afterwards describe a particular structure in which they are embodied.

Referring to Fig. 1, A is a bar of iron, which is fixed in position, and B is another bar of iron which is freely movable toward and from the bar A. In the diagram the bar B is shown as depending from a stem C, flexibly suspended at D. Any arrangement by which the bar B is perfectly free to vibrate will answer the conditions. A magnetic flux is normall impressed to pass between the bars A and in any suitable way, as, for 40 exam le, by means of the permanent magnet E, w ich contacts with the bar A, and is closely ad'acent to the bar B alo a surface thereof w ich is parallel to the irection of movement, so that no component of force is produced to move B except the attraction of the pole piece A. The bar B may be balanced against moving toward A in any suitable way, as, for example, b another pole A and magnet E, similar to and E respec- 50 tively, but on the other side of B.

G is a ma etic windin'g or coil which sur rounds the ars A and B, and is adapted to superpose its magneto motive force upon that of the permanent magnet E. The essential characteristic is that the bars A and are sufficiently large to carry the superposed flux of the coil G and the magnet E without becoming saturated. When telephonic or voice currents pass through the winding G, under these circumstances, practieally the entire energy thereof-is transformed into forces of attraction and repulsion between the bars A and B. This is because the full electrical energy goes to the production of I magneto motive force and the full magnetic force goes into the production of 'olar attraction between the bars A ant B,in other words, into ordinary mechanical force. The only problem remainin therefore, is to transform this force into de ivered energy at a diaphragm. Now we have seen that the bar B must be suiliciently massive to carry the magnetic flux, and under these circumstances it is so massive that it does not have a wide amplitude of movement under the im ressed force by reason of its great inertia. It lies all the theoretical energy, however, because what it lacks in amplitude it makes up in mass, and the product or momentum is the theoretical maximum due to the voice currents. The bar B has a movement, therefore, which represents in kinetic energy, practicallv all the energy of the voice currents. The remaining problem is to transform this energy into operation of a diaphragm of just sufficient size and amplitude to give the most efficient transmission of the energy to the air. Such a diaphragm I may form of thin mica, supported in a sound box, and I make use of a lever connection between the bar- B and this diaphragm, such lever connection having a multiplying effect exactly suited to the requirements. In other words, the multiplying effect is such as to multiply the movement of limited am litude of the bar B to just the extent whic is required to move a diaphragm suited to the most perfect sound reproductive efficiency. By the embodiment of these theoretical principles it is evident that the highest possible re roductive efficiency is secured.

. I will now consider the details of the mechanical structure which embodies the foregoing princi Ice. The magnets E, E, of the above escribed diagrammatic representation are in this case formed by the sheet steel ri sections or segments 1 and 2, each of whic has an angular extent of slightly less than a complete circumference. A number of rings are riveted or otherwise secured together to form the magnet, thereby producing a compound magnet of greater strength. To one end of each of the ring sections 1 and 2 is fastened a polar extension 3, which may be of steel or soft iron, and which has an inwardly projecting stud 4, also of soft iron. In practice the inwardly extending studs 4 are formed by screws passed through the polar extensions 3, so as to fall in alinement with one another. These screws correspond to the pole pieces A, A, of the diagrammatic representation above set forth.

5 is a central common pole piece of both m nets havin an extension 6 in proximity to t c axis joining the poles 4.

7 denotes coils corres ondirig to the coils G, G, of the above diagrammatic representation, and 8 designates the movable part or armature which vibrates between the pole pieces 4. By this arrangement the armature 8 has exactly the same relation between the poles 4 as the bar B between the poles A, A, of Fig. 1. The armature is also polarized in the same way, that is to say, it has poles of the same character at its two ends, and a single opposite ole at the middle. This polarity is induce by the permanent field magnets which magnetize the two studs 4 of one polarity, and the,intermediate extension 6 of the opposite polarity. While this particular arrangement of the magnet poles is not absolutely essential, it has a very great ractical advantage. This advantage ist at there is no ossibility of the flux produced by either coi traversing the armature from one end to the other. If the flux due to the coils or windings traversed the armature from one end to the other, any variations therein would produce changing forces of attraction at both ends of the armature, instead of one end only. If the forces of attraction vary at both ends simultaneously, the effects would neutralize one another, and impair the efficiency. But by having the armature polarized in the manner already described, this effect is absolutely prevented, since the flux of each side is kept entirely separate from the other side, so that there is no neutralization of the forces. In other words, the effects ofboth windings are added together without any. reactions being produced to lessen the efficiency. The armature 8 is supported s'o as,to vibrate freely in a longitudinal direction between the ole pieces 4. The means which I employ or su porting the armature give the same specia characteristics in its vibratory movement, and which form an important feature of the invention. Knife'edges '11 are suported by a fixed frame. This frame is ormed. by a standard 13, projecting upward from the base, and having studs 14, which support a box 15. The knife edges 11 are fixed to the box 15, and the springs 12 are borne upward by screws 16, which extend through lateral arms 16 on said box. In this way the armature 8 is held so as to be freely movable toward and.

from the pole pieces 4, but immovable in any other direction. This arrangement by which the armature 8 is held against the knife edges 11 by the springs 12 not only serves to permit the armature to have a to, and fromovement, but also exerts a certain "force to keep the armature in its normal central or mean position. The tension by which the armature is held in. its central osition may be increased or diminished by adjusting the screws 16. It is important to have a certain tension for this purpose, in order that the armature mayacquire the same movements as those of an ordinary sound wave. The sound of an ordinary wave is transmitted by the air, the molecules of which are elastically impelled in a certain relation, and in transmitting asound wave the molecules are displaced on one side or the other of this position. The armature 8 is therefore correspondingly impelled by the springs 12 into a mean position, and is displaced to one side or the other by the forces of attraction of the magnetic system. As will later appear, a diaphragm is also used which by its own elasticity tends to take a certainnormal position. The springs 12 enable the armature to operate properly without relyin on the diaphragm to which it-is connecte in a manner which will be presentliy set forth.

17 in icates a stem or arm extending from the blocklO This arm is much longer than the stem 9, so that the movements of the armature 8 are multiplied at the extremity of the extension arm 17. The ratio is made a certain value, depending on several factors. The factors which determine this ratio will be later more particularly considered. The upper end of the arm 17 is fixed to diaphragm 18, which is referably of thin elastic-material, such as siieet mica, and which is clampedbetween rubber rings 19, within the box 15. The diaphragm 18 is made so thin and so elastic as to vibrate very easily and with almost perfect elasticity, so that a minimum amount of the energy of its vibration goes intomolecular movement or heat, and a maximum amount of the energy of vibration is delivered to the air in the form of sound. In other words, it is made so that it vibrates with sufficient amplitude .to impress sound vibrations on the air with the greatest eflicienc and at the same time is made suflicient y elastic so that it is able to acquire all of the fine vibrations of ordinary speech. Neither of these effects is secured except at extremely low efficiency in an ordinary ferrotype tele hone diaphragm, and it is obvious that t e diaphra m 18 of the present invention may be made of such material, size and thinness as to attain the very best possible results, unimpeded by any electrical or magnetic considerations. In practice mica clamped between the rubber rings 19, is found to give satisfactory results. The box 15 therefore constitutes} sound box,

and has tubular extensions or "sound delivery openings 20, to which rubber tubes may be attached, or a sound horn, or any other sound delivering device.

I will now consider the leverage ratio of the extension arm 17 to the stem 9. As has been pointed out in the preliminary part of this specification, the vibrating piece or armature 8 should be made with a quite considerable amount of iron in order that it may carry'the entire magnetic flux roduced by the various magneto motive l drces. This movement, and that the diap ragm 18, by

condition attained, it is evident that the actual forces impressed on the armature result in certain vibrations thereof which are less in proportion to the size of the armature, but which correspond to a certain energy of vibration in all cases. Now on the other hand, it is found that the very best efficiency of sound transference is obtained from the diaphragm 18 to the air when such diaphragm is made of a certain size, and has a certain amplitude of vibration. It is merely necessary to ascertain this vibration, amplitude and the actual vibration of the armature 8 under the magnetic forces, and then proportion the ratio of the stems 9 and 17 to the respective values. In the drawings the proportion is about the best which I have found in )ractice. By this arrangement the soun producing diaphragm and the entire electrical and magnetic systems are kept absolutely separate and distinct from one another. Each may be designed and constructed in accordance with the best theoretical principles and the connections, links, levers, or means to transmit the motion from one to the other afterwards applied in the most direct and convenient way.

The magnetic coils 7 may be connected in series or multi 1c, the multiple arrangement being ordinariy preferable, with any telephone circuit, or circuit in which voice currents are produced. The current fluctuations are transformed into correspondim fluctuations in magneto motive force, an this magneto motive force is transformed into corresponding fluctuations in the flux through the armature with almost perfect efficiency by reason of the large mass of the armature. This varying flux is accompanied by corresponding variations in the force of attraction, so that all of the energy of the voice currents goes into vibration of the armature. This energ is then transferred without substantial oss to the mica diaphragm which is adapted to transform the vibrations into sound waves with the best efficiency. In practice, of course, there is a slight unavoidable loss at each stage due to mechanical friction and other causes, but such slight losses amount only to a very small per cent.,so that the a paratus attains ractically the perfect con ition of delivermg in actual sound the entire energy of the voice current fluctuations.

It has already been ointed out that the armature 8 is impelle by the springs 12 elastically into a certain mean osition of its its own elasticity normally acquires a certain mean or normal position corresponding to the mean position of the armature and to a state of rest of the system. The forces due to the varying currents in the windings 7 are applied to the armature, and act together to assist one another to displace the armature to one side or the other of its mean position. The action is entirely symmetrical, the motion corresponding exactly to the molecular movement of the air during a sound wave. The resiliency of the springs 12 influences the movement of the armature to just the extent that the elasticity of the air influences the movement of the molecules. The action is entirely different from that of the ordinary telephone receiver in which the forces are all from one side and by which the diaphragm is constantly arched inward. The result is to obtain perfect .purity in the sound delivery. This is attained because the symmetrical and balanced conditions of the constant and the variable forces of the entire system are exactly analogous to those of the air molecules in sound transference. The diaphragm 18 and the armature are designed to vibrate symmetrically on either side of their mean positions, and the forces are adapted to produce such vibrations symmetrically on each side of the mean positions.

The tension of the balancing spring 12, is such as to ive the movable system a natural period of VfiflltlOIl higher than that of speech or musical notes which the receiver will be called upon to reproduce.

While I have articularly described this invention as app ied to the ophration of a telephone receiver, I do not desire to be limited or restricted to this particular use, since it is obvious that the features of the construction are equally applicable to a telephone re lay or any-other acoustic apparatus where a part is mechanically vibrated by voice currents.

What I claim, is z 1. In a telephone receiver, a pair of magnets forming parts of separate magnetic circuits, a lon itudinally movable armature for each of said circuits, and means movable therewith for transmitting to a distance the movements of the armature corresponding to variations in the flux of said magnetic circuits.

2. In a telephone receiver, a pair of fixed magnets having one pole in common, their other poles being oppositely disposed with respect to each other, and an armature substantially closing the gaps between the poles of said magnets and movable toward and away from the 0 positely disposed poles and across the face of the common pole.

3. In a telephone receiver, a magnet and an armature therefor movable toward and away from one pole and across the face of the other pole.

4. In a telephone receiver, a diaphragm, an armature havin a lever connection there with whereby its v1 ration is transmitted to the diaphragm, a pair of magnets each forming separate magnetic circuits in connection with and substantially closed by said arms.-

ture, whereby the armature is balanced by the combined attraction of'said magnets, and means whereby telephonic currents have their energy transformed into magneto mo tive force and impressed into a varying magnetic fiux through said armature whereby the armature vibrates with substantially all the energy of the telephonic currents.

5. In a telephone re'ceiver,.a pair of magfliknets'each substantially ring-shaped and having an interrupted portion, a pair of studs projecting inward therefrom and 'constitut ing (poles, an extension also extending inwar and constituting a pole opposite to that of said first mentioned poles, and an armature supported to move toward and from said first mentioned poles and in proximity to said last mentioned pole,

6. In atelephone receiver, a pair of magnets each generally ring-shaped and having an interrupted portion, poles extending inward therefrom, an armature mounted to move in the direction of said poles, and an additional extension from each of said magnets and having 0 posite polarity to said first mentioned -po es and extending into close proximity to an intermediate portion of said armature.

7. In a telephone receiver, a pair of ringshaped magnets each having an interrupted portion, a sound box between said magnets, an armature sup orted by said sound box, polar extensions Tom said magnets extendlng into proximity to said armature at three points thereof, and a plurality of coils adapted to superpose their magneto motive force on that of said magnets.

8. In a telephone receiver, a plurality of magnets each having an interru ted portion, three polar extensions from sai magnets, an armature mounted to move between two of said extensions and in proximity to said third extension, and magnetic coils for superposing a magneto motive force upon that of said magnets.

-9. In a telephone receiver, a pair of magnets having twosalient poles and one consequent pole, said salient poles being of like polarity, an armature mounted to move in a direction normal to said salient poles and tangential with respect to said consequent pole and coils adapted to impress their magneto motive force on the flux of said field.

10. In a telephone receiver, an armature,

knife edges adapted to support said armature to have a vibratory movement, a pair of springs connected to said armature to hold the same against said knife edges and to re siliently impel it into a mean position of its movement, means for creating a magnetic field to include said armature, and means for su erposing a magneto motive force on said feih to change the flux thereof.

11. In a telephone receiver, means forcre- 6 ating a magnetic field, an armature therein,

a bar fixed to said armature, a ,pair of kn fe edges adapted. to support said bar, a pair of resilient springs projecting from said ar, and means for tensloning said springs to sound box-,-a-bar-- supported by said knife edges and-rigidly connected to said armature, a pair of sprin 's projecting from said bar, means for impelling said springs toward said sound box whereby said bar is pressed against said knife edges and normally held in a mean position of its movement, and a stem projecting from said bar and attached to said diaphragm.

13. In a telephonic apparatus, a magnet in a circuit adapted to be traversed by voice currents, a doubly polarized armature therefor, an element for amplifying the move ments of said armature and means for propagating the effect of such amplification.

14. In a telephone receiver, a magnet, an armature therefor movable toward and away from one pole and across the face of the other pole and a connection for transmitting to a distance the movements of the armature.

15. In a telephone receiver, a pair of magnets and an armature movable toward and away from one pole of each magnet and across the face of the other pole thereof.

16. In a telephone receiver, a pair of magii'et's anarmature movable toward and away from one pole oieagh magnet andacross the face of the other ole-thereof and resilient means for normalfy holdingsaidnarmature member in definite relation to said magnets w 17. In a telephone receiver, a pair of magnets and an armature adapted to be influenced by voice currents, said armature bein elongated and longitudinally movable, am. said magnets being capable ,of moving said armature in opposite directions away from its normal or mean position, an element having an amplified movement with respect to said armature, means for propagating the effect of such amplification, and resilient means separate and distinct from said propagating means and operating to perform the function of directing the armature from either of its extreme positions into or toward its normal or mean position.

. 18. In a telephone receiver, a magnet and armature adapted to be influenced by the voice currents, said armature being elongated in the direction of the flux of the magnetic circuit and longitudinally movable, an element having an amplified movement with respect to said armature, and means 'for propagating the effect of such amplification.

19. In a telephone receiver, a magnet adapted to be influenced by the voice currents, a diaphragm, an armature elongated Finthe directionofithefiuzi of the magnetic circuit and longitudinally movable, and a multiplying connection between the armature and diaphragm.

20. In a telephone receiver, a pair of magnets forming parts of separate magnetic circuits, an elongated longitudinally movable "1116111081 for-min an armature for each of said circuits, said armature being polarized at each end with similar poles, an element liavin an amplified movement with respect to sai armature, and means for propagating the effect of such'amplification- 21. Ina telephone receiver, amagnet, a coil through which the voice currents pass and adapted to vary the magnetic flux of said said armature and said diaphragm.

ture, in the presendebftwo witnesses.

HARVE R. STUART.

Witnesses:

H. D. KENNEDY, CHAS. J. WRIGHT.

an armature, an a lever connection between In witnessiwher eof, I subscribe mgr igma 

